The present invention relates generally to imaging lens arrangements. More specifically, the present invention relates to imaging lens systems that provide improved lens properties within a low light environment.
Conventional low light lens systems are typically designed for use in cameras. These lenses provide adequate lens properties when the object being imaged is positioned relatively far from the lens (e.g., greater than 600 mm). For example, these conventional low light lens systems have adequate relative illumination at relatively large object-to-lens distances and poor relative illumination characteristics at closer distances (e.g., less than 600 mm). That is, for short distances the illumination collection efficiency varies significantly across the field of view. For instance, conventional lenses typically have only a 70% illumination efficiency across a 26 mm field of view at the image plane. Additionally, certain imaging characteristics are typically sacrificed in the design of a conventional lens system to reduce the costs of manufacturing the lens. For example, the illumination efficiency or xe2x80x9crelative illuminationxe2x80x9d tends to decrease dramatically at the edges of the field of view (commonly referred to as vignetting). Conventional low light lens systems also tend to have significant optical aberration characteristics. Although the non-uniform relative illumination and aberration characteristics of conventional lens systems are not serious problems in certain applications (e.g., photography for hobbyists), these characteristics are unacceptable in other applications.
For instance, conventional lens systems are inadequate for one specialized type of imaging that involves the capture of low intensity lightxe2x80x94on the order of individual photonsxe2x80x94from a light emitting sample, such as a small animal injected with a luminescent substance. The source of the light indicates portions of the sample where an activity of interest may be taking place, such as the growth of malignant tumors. Specialized in-vivo imaging applications may include one or more representations of emissions from internal portions of a specimen superimposed on a photographic representation of the specimen.
Such imaging applications present particular challenges to the design of the lens system. In this type of application, the object to be imaged is typically positioned relatively close to the lens system (e.g., 200 to 400 mm) so that the relatively small object fills the entire field of view. Additionally, relatively small features of the object are typically examined. For example, a mouse""s brain may be examined for tumors. In this type of application where small image features must be accurately distinguished across the entire sample, it is important that the lens system provide substantially constant relative illumination, low vignetting, adequate spatial resolution, and minimal aberration characteristics at relatively close object-to-lens distances. Unfortunately, currently available conventional lens systems fail to meet the needs of many low light applications, such as imaging of a light emitting biological sample.
Accordingly, there is a need for a lens system that has a relatively constant relative illumination and insignificant aberration problems while imaging an object positioned relatively close to the lens system. Of course, it is also preferable to design such lens systems at a reasonable total cost.
Accordingly, the present invention provides an improved lens system for low light applications. This improved low light lens system is designed for any suitable low light application, such as the above described biological imaging application. In one embodiment, a finite conjugate lens system is disclosed. The lens system includes, in order from a camera side to an object side, a first lens group and a second lens group. The first and/or second lens groups are adapted so that when light is passed from the object side to the image side, a substantially sized region of collimated light is formed between the first and second lens group. Preferably, the first and/or second lens groups are adapted to demagnify an object at the object side.
Preferably, the region of collimated light space is greater than about 25 mm. In one implementation, the region of collimated light space is adapted to receive one or more filter wheel(s). In one aspect, the first and second lens groups are configured to provide a field of view at the image plane having a diameter that is less than or equal to about 36 mm. In a specific implementation, the field of view diameter is less than or equal to 26 mm. Preferably, the lens system also includes a third lens group configured to provide a plurality of demagnification levels. In one implementation, the third lens group includes a plurality of lens sub-groups mounted on a turret. In a specific example, the third lens group includes a plurality of lens sub-groups each configured to provide a different demagnification level.
In another embodiment, the lens system satisfies the following conditions (1) and (2):
0.9 less than f/# less than 1.1xe2x80x83xe2x80x83(1)
0.9 less than RI less than 1.0xe2x80x83xe2x80x83(2)
where f/# and RI are focus number and relative illumination respectively, and both the f/# and the RI are obtained across a field of view at the image plane having a diameter that is less than or equal to about 26 mm. Both the f/# and RI are obtained for demagnification levels between 1.25xc3x97 and 10xc3x97. In another implementation, the system includes a detector for imaging light received through the first and second lens groups and a shutter and/or iris for controlling light exposure time on a detector. The shutter and/or iris is positioned between the first lens group and the second lens group. Preferably, the shutter and/or iris is motorized.
In an alternative embodiment, a lens system is disclosed. The system includes, in order from a camera side, a first lens group and a second lens group. The lens system satisfies the following conditions (1) and (2):
0.9 less than f/# less than 1.1xe2x80x83xe2x80x83(1)
0.9 less than RI less than 1.0xe2x80x83xe2x80x83(2)
where f/# and RI are focus number and relative illumination respectively, and both the f/# and the RI are obtained across a field of view at the image plane having a diameter less than or equal to about 26 mm. Both the f/# and RI are obtained for demagnification levels between 1.25xc3x97 and 10xc3x97.
In yet another embodiment, an imaging system for capturing an image of a sample is disclosed. The imaging system includes an imaging box designed to prevent most light from entering an inside compartment of the box in which an object to be imaged may be placed and a lens system integrated within the imaging box through which light emitted from the object to be imaged passes. The lens system satisfies the following conditions (1) and (2):
0.9 less than f/# less than 1.1xe2x80x83xe2x80x83(1)
0.9 less than RI less than 1.0xe2x80x83xe2x80x83(2)
where f/# and RI are focus number and relative illumination respectively, both the f/# and the RI are obtained across a field of view at the image plane having a diameter less than or equal to about 26 mm. Both the f/# and RI are obtained for demagnification levels between 1.25xc3x97 and 10xc3x97. The imaging system further includes a detector for receiving the emitted light and generating an image of the object.